This invention concerns a method of and apparatus for improving control of the distribution of paper stock in a paper or board making machine.
Conventionally, paper stock is distributed onto a forming section of a paper or board making machine by passing it through a head box, which comprises an inlet chamber, known as an inlet header, connected to a nozzle section by way of a plurality of tubes or ducts.
Some known types of head box as described, for example in EP-A-0 635 599 and U.S. Pat. No. 5,545,293, are more complex in structure and the plural tubes connecting the inlet header to the nozzle section or comparable discharge duct are arranged in a series of groups disposed side by side and one above the other. Furthermore, a first series of such groups lead from the inlet header into an intermediate chamber, to which an attenuation chamber for purposes of pressure equalization is connected, while a second series of such groups lead from the intermediate chamber into the nozzle or discharge duct.
The present invention is applicable to both the simpler and more complex types of head box.
The aforesaid specifications describe how, in order to regulate the distribution of paper stock, namely paper pulp suspension, a dilution flow may be introduced into at least one of the tubes of the second series. In particular this dilution flow, which may comprise only water, is introduced into a mixing chamber section of a tube, which section leads immediately from the intermediate chamber in the direction of flow. Moreover, this dilution flow may enter the tube annularly from around a narrower pipe through which the original paper stock is fed into the mixing chamber.